This invention relates to apparatus for pulverizing, i.e., grinding, material, and more specifically to a coiled spring system that is particularly suited for embodiment in a bowl mill wherein the coiled spring system is operative for purposes of establishing the magnitude of the forces which the grinding rolls of the bowl mill exert on the coal for purposes of effectuating the pulverization of the coal.
An essential component of any steam generation system of the type, which utilizes pulverized coal as a fuel, is the apparatus in which the coal is pulverized so as to render it suitable for such usage. Although the prior art is known to have employed various types of apparatus for purposes of accomplishing coal pulverization, one form of apparatus in particular, which has frequently been used for this purpose, is that commonly referred to as a bowl mill by those in the industry. The bowl mill obtains its name principally from the fact that the pulverization, i.e., grinding, of the coal that takes place therewithin occurs on a grinding surface which in configuration somewhat resembles a bowl.
By way of illustration, reference may be had to U.S. Pat. No. 3,465,971 which issued Sept. 9, 1969 to J. F. Dalenberg et al. and which is assigned to the same assignee as the present invention for a showing of a prior art form of bowl mill. This patent contains a teaching of both the nature of the construction and the mode of operation of a bowl mill that is suitable for use for purposes of effectuating the pulverization of the coal that is used to fuel a coal-fired steam generator. As taught by this patent, the essential components of such a bowl mill are a body portion, i.e., housing, within which a grinding table is mounted for rotation, a plurality of grinding rolls that are supported in equally spaced relation one to another in a manner so as to coact with the grinding table such that the coal disposed on the surface of the grinding table is capable of being ground, i.e., pulverized, by the rolls, coal supply means for feeding to the surface of the grinding table the coal that is to be pulverized in the bowl mill, and air supply means for providing to the interior of the body portion the air that is required for the operation of the bowl mill.
In order to satisfy the demands of a coal-fired steam generation system of conventional construction for pulverized coal a multiplicity of bowl mills of the type shown in the aforereferenced patent are commonly required to be employed. Further in this regard, it is noted that the individual capacity of each of these bowl mills may range up to a capacity of one hundred tons of pulverized coal per hour. In addition to possessing a capability of operating at their maximum capacity, these bowl mills must also have the ability to operate at less than full capacity, i.e., at some percentage thereof, e.g., 25%, 50%, 75%, etc. Accordingly, this fosters a further requirement that the bowl mill be capable of exerting the requisite degree of grinding force regardless of the rate of output at which the bowl mill is operating. Here note is taken of the fact that variations in the output provided from the bowl mill are normally accomplished by varying the amount of coal that is fed to the grinding table, while the speed of rotation of the grinding table is made to remain substantially constant.
The depth of coal that is disposed on the grinding table is a function of the output rate at which the bowl mill is performing. In addition, the depth of coal that is present on the grinding table has an effect on the amount of grinding force being exerted on the coal by the grinding rolls. Obviously, therefore, it is important that if the grinding rolls are to apply the requisite degree of force needed to effect the pulverization of the coal, consideration must be given to the existence of this relationship between the grinding force exerted by the grinding rolls and the depth of coal on the grinding table.
The journal loading, which dictates the amount of grinding force that the grinding rolls exert on the coal, has heretodate been provided either through the use of hydraulic systems or through the use of mechanical springs. One such arrangement of mechanical springs can be found depicted, for example, in the patent which was referred to above previously. In accord with a showing contained in this U.S. patent, each grinding roll is urged towards the surface of the grinding table by means of an adjustable spring. To this end, there is selected for use for this purpose, a mechanical coil spring that possesses the design characteristics desired; namely, a spring that is capable of urging the grinding roll toward the grinding table surface in such a manner that the grinding roll exerts a predetermined grinding force on the coal disposed on the table, when the coal is of a predetermined depth on the table.
As an alternative to the use of mechanical coil springs for purposes of providing the journal loading, the prior art on occasion has turned to the employment of hydraulic systems. U.S. Pat. No. 4,002,299, which issued on Jan. 11, 1977 to C. J. Skalka and which is assigned to the same assignee as the present application, is directed to one arrangement of such a hydraulic system. In accord with the teachings of this patent, a system is provided wherein grinding rolls have a hydraulic loading applied thereto. More specifically, the hydraulic loading on the grinding rolls is established by means of hydraulic fluid that is fed under pressure to the grinding rolls. Moreover, through the use of a servo system, changes in the hydraulic pressure are automatically effected as the mill output increases or decreases.
Whether the journal loading is accomplished in a bowl mill by means of a hydraulic system or by means of a mechanical spring system is commonly determined before the bowl mill is manufactured. Furthermore, once the bowl mill has been manufactured with a particular form of journal loading system, this is the form of journal loading system that the bowl mill embodies during the remainder of its useful life. Namely, the conventional practice has been one in which a bowl mill which at the time of its original manufacture was made to embody, for example, a hydraulic journal loading system will always embody a hydraulic journal loading system. On the other hand, situations have been known to have arisen in which it would have been desirable to replace one form of journal loading system with another form of journal loading system. More specifically, in the case of a number of the more recent of such instances it would have been desirable to be able to replace a hydraulic journal loading system with a mechanical spring system. However, heretodate, primarily because of the basic nature of the differences, both in terms of the nature of the construction and the mode of operation thereof, that has existed between a hydraulic journal loading system and a mechanical spring journal loading system the owner of the bowl mill has not had available to him the option of being able to replace a hydraulic system with a mechanical spring system. A need has thus been evidenced for a new and improved form of coiled spring system which could be utilized in a bowl mill as a journal loading system, but which most importantly would be capable of being utilized as a retrofit for a hydraulic journal loading system in a bowl mill.
It is, therefore, an object of the present invention to provide a new and improved system operable for establishing the journal loading on the grinding rolls of a bowl mill that is suitable for use to pulverize coal.
It is another object of the present invention to provide such a system that is operative to establish a mechanical spring journal loading on the grinding rolls of a bowl mill suitable for use to pulverize coal.
It is still another object of the present invention to provide such a mechanical spring system for establishing the journal loading on the grinding rolls of a bowl mill that is capable of being utilized as a retrofit for a hydraulic journal loading system in an existing bowl mill.
A further object of the present invention is to provide such a mechanical spring system for establishing the journal loading on the grinding rolls of a bowl mill that is characterized by the fact that lower forces are exerted thereby on the lower main vertical shaft of the bowl mill.
A still further object of the present invention is to provide such a mechanical spring system for establishing the journal loading on the grinding rolls of a bowl mill that is characterized by the fact that the spring portion thereof is suitably positioned such that minimal influence is exerted thereupon by the operating conditions which exist within the bowl mill.
Yet another object of the present invention is to provide such a mechanical spring system for establishing the journal loading on the grinding rolls of a bowl mill that is characterized by the fact that less maintenance is required thereby.
Yet still another object of the present invention is to provide such a mechanical spring system for establishing the journal loading on the grinding rolls of a bowl mill that is relatively simple to manufacture and operate, as well as being relatively inexpensive to provide.